JPH0982637A - Method for manufacturing amorphous semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out a free designing of an optical band gap of an amorphous thin film to attain a high quality of the thin film manufacture by a method wherein the amount of atomic state hydrogen fed to the surface of the semiconductor thin film is set within a specific range by the step exposing the thin film by a plasma made of hydrogen gas. SOLUTION: An RF discharging electrode to form hydrogen plasma is provided separately from a film forming mechanism. Next, a step to form a specific film-thickness by chemical vapor evaporating process and step to expose a formed amorphous semiconductor thin film to a plasma are repeated. At this time, the amount of the atomic state hydrogen is specified to at least 1×10<15> pieces/cm<2> to 5×10<15> pieces/cm<2> . Through these procedures, hydrogen can be effectively fed to any non-coupled bond in a film generation of which has been uncontrollable by normal film-forming method, as the result the defective density can be greatly decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of an amorphous solar cell, and more particularly to a technique for improving the quality of an amorphous semiconductor thin film that constitutes the amorphous solar cell.

[0002]

2. Description of the Related Art Amorphous silicon solar cells have already been put to practical use as a low output energy source for driving calculators, clocks, and ventilation fans of automobiles. However, as an energy supply source with a large output of 10 W or more, such as a solar power generation application, it cannot be said that its power generation performance and stability are sufficient.
For this reason, it is not possible to sufficiently reduce the cost of power generation, which is extremely important as an element of energy supply, and this is the largest requirement that prevents the spread of amorphous silicon solar cells for electric power.

Plasma CV using a metal hydride compound such as silane is used for manufacturing an amorphous solar cell.
It is a film forming method by D. This is because a metal hydride compound such as silane is flown into a vacuum chamber for film formation controlled to a pressure of 10 mTorr to 1 Torr, and decomposition is caused by plasma, and a substrate placed in the vacuum chamber for film formation is placed. It forms a thin film, and has the advantage that it can be formed uniformly over a large area. In addition, since a thin film of amorphous silicon or the like having an optical characteristic with a high absorption coefficient for sunlight is formed by this method, it is an optimum method for those requiring a small film thickness. It can be said to be a membrane method.

Also, since a laminated thin film having different optical and electrical properties can be formed by the same film forming method called plasma CVD, it can be prepared easily by changing the gas species and film forming conditions. It is possible to form. Further, it is also possible to form continuously by arranging devices having a similar vacuum chamber for film formation in series.

As described above, although the film formation by plasma CVD is an excellent method for forming an amorphous silicon thin film, what plays a major role as a factor that determines the performance of these thin films is in the film. It is hydrogen contained. The optical bandgap is greatly influenced by the content of hydrogen in the film and the bonding form, and the transport characteristics of carriers are greatly affected. Further, it is known that the presence of hydrogen in the film plays a large role in reducing the defect density, but it is not possible to control the hydrogen amount itself for the purpose of reducing the defect density. It was a reality. Therefore, controlling the hydrogen content and the hydrogen bond morphology in the film has been an important issue to date.

However, in general, in the film formation method by plasma CVD, the hydrogen content in the film and the hydrogen bond form are indirectly controlled by the gas flow rate, the pressure during film formation, the temperature, the concentration of the diluting gas, and the like. Therefore, the reality is that a secondary film forming method must be used. Further, not only for amorphous silicon, but also for amorphous silicon germanium and amorphous silicon carbon, the hydrogen content contained in the film and the hydrogen bond morphology are not sufficiently controlled, It is also an important issue for improving the quality of these membrane chambers. In particular, the optical bandgap 1.
For amorphous silicon thin films of 8 eV or more, a method using hydrogen dilution has been used so far. As a result, a film having an optical band gap higher by about 0.6 eV was obtained as compared with the conventional film of around 1.77 eV, and as a result of applying the obtained film to an amorphous solar cell, it was high. It was possible to obtain the one that obtains the open circuit voltage. However,
In order to obtain a higher open-circuit voltage, it is necessary to obtain a film having a higher optical band gap. Furthermore, the defect density of these films is required to be low.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the optical band gap of an amorphous thin film can be freely designed by directly controlling the hydrogen content and the hydrogen bond morphology in the film by a chemical vapor deposition method. It is possible to achieve high quality thin films by reducing defects and to improve the conversion efficiency of thin film solar cells, especially the method of forming materials for improving open-ended voltage and fill factor. The purpose is to propose.

[0008]

The present invention is specified by the following matters. (1) A method for producing an amorphous semiconductor thin film, which comprises repeating a step of forming a semiconductor semiconductor thin film by a chemical vapor deposition method using a thin film raw material gas and a step of exposing the thin film with plasma consisting of hydrogen gas. Then, by the step of exposing the thin film with plasma composed of the hydrogen gas,
The amount of atomic hydrogen supplied to the surface of the semiconductor thin film is 1 × 10
^A method for producing an amorphous semiconductor thin film, which comprises not less than ¹⁵ / cm ^{2 and not} more than 5 × 10 ¹⁵ / cm ² . (2) The method for producing an amorphous semiconductor thin film according to (1), wherein the amount of bound hydrogen in the semiconductor thin film formed by the chemical vapor deposition method using a thin film raw material gas is 25 atomic% or less and 5 atomic% or more. . (3) The method for producing an amorphous semiconductor thin film according to (1) or (2), wherein the thickness of the semiconductor thin film formed by a chemical vapor deposition method using a thin film raw material gas is 1 nm or more and 6 nm or less. . (4) The amorphous semiconductor thin film is a hydrogenated silicon amorphous thin film, a hydrogenated germanium amorphous thin film, a hydrogenated carbon amorphous thin film, a hydrogenated silicon germanium amorphous thin film, or a hydrogenated silicon carbide amorphous. The method for producing an amorphous semiconductor thin film according to any one of (1) to (3), which is a thin film. (5) The chemical vapor deposition method is a photo CVD method or a thermal CVD method.
Method, plasma enhanced CVD method, laser enhanced CVD method, or reactive sputtering method, according to any one of (1) to (4). (6) The raw material thin film gas is a silicon hydride compound Si _n
H _{2m + 2} , hydrogenated germane compound Ge _n H _{2m + 2} , hydrocarbon C
_n H _{2m + 2} , or a compound or derivative in which hydrogen of these compounds is replaced by a chlorine atom or a fluorine atom, or a derivative thereof, wherein the amorphous semiconductor thin film is any one of (1) to (5). Manufacturing method. (7) The method for producing an amorphous semiconductor thin film according to any one of (2) to (6), wherein the source gas contains hydrogen or an inert gas. (8) The method for producing an amorphous semiconductor thin film according to (7), wherein the inert gas is a rare gas selected from He, Ne, Ar, Kr or Xe.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The present invention basically uses a single metal hydride compound gas, preferably containing hydrogen or a diluent gas such as an inert gas, to form an amorphous semiconductor thin film containing high quality hydrogen. When a step of forming a predetermined film thickness by a chemical vapor deposition method and a step of exposing the formed amorphous semiconductor thin film to hydrogen plasma are repeated, it is generated during discharge of hydrogen gas and supplied to the substrate surface. The amount of atomic hydrogen is 1 × 10 ¹⁵ pieces / cm ² or more and 5 × 10 ¹⁵ pieces / cm ² or less.

The method is generally formed by the following procedure. That is, first, preferably, a predetermined film thickness is formed by a chemical vapor deposition method using hydrogen or a metal hydride compound gas containing an inert gas. The chemical vapor deposition method used here is a photo CVD method, a thermal CVD method, a plasma enhanced CVD method, a laser enhanced CV.
D method and reactive sputtering method. The metal hydride compound gas, silicon hydride compound Si _n H _{2m + 2,} hydrogenated germane compound Ge _n H _{2m + 2,} tin hydride compound Sn _n H
_{There are 2m + 2} and C _n H _{2m + 2} . Further, as the material of these metal hydride compounds, it is also possible to use compounds in which hydrogen atoms are replaced by chlorine atoms or fluorine atoms or derivatives thereof. Further, as impurities for forming a semiconductor having different electrical properties, a boron hydride compound B _n H _{2m + 2 and a} phosphorus hydride compound P _n H _{2m + 2} and an arsenic hydride compound As _n H _{2m + 2 are used.}
Can also be used with the metal hydride compound gas.

The raw material gas may be used alone without dilution, but may be diluted with hydrogen or an inert gas. In case of diluting gas such as hydrogen, the maximum is about 100 times.
(For example, use a flow rate of 1 sccm for silane and 100 sccm for hydrogen.
). Further, as the inert gas used similarly to hydrogen, there are rare gases such as He, Ne, Ar, Kr, and Xe. It should be noted that the ratio of the dilution rate with these gases is not particularly limited.

In a system containing these gases, evacuation is performed from the stage of completing the step of forming the amorphous semiconductor thin film by the chemical vapor deposition method to the step of exposing to the hydrogen plasma. As a result, it is possible to minimize the influence of residual film forming gas before the step of exposing to hydrogen plasma after the step of forming a film.

On the contrary, when this vacuuming is not inserted between the film forming step and the step of exposing to hydrogen plasma, the film forming gas flown in the film forming step remains for the residence time and a large amount. Since it is in a state of being diluted with the hydrogen gas, the crystallization is likely to occur. Therefore, the result is deviated from the purpose of manufacturing the intended high-quality amorphous semiconductor thin film.

The hydrogen content of the amorphous semiconductor thin film formed in the film forming step is preferably less than 25 atomic% and 5 atomic% or more. There are the following two typical cases of forming an amorphous semiconductor thin film having a hydrogen content of less than 5%. That is, a temperature high enough to release hydrogen contained in the film, specifically, the substrate temperature 38.
This is the case when the film is formed at 5 ° C. or higher. Further, in the case of performing film formation in a hydrogen diluted state containing excess hydrogen, in this case, the bonding morphology in the amorphous semiconductor thin film is significantly changed, and as a result, the amount of bound hydrogen is significantly reduced, Microcrystallizes.

First, when the substrate temperature is high, that is, when the substrate temperature is 385 ° C. or higher, hydrogen desorption is stronger than hydrogen invasion during the film formation process. Therefore, exposure to hydrogen plasma under the same temperature conditions as the film formation can no longer play an effective role. Also, in the case of causing microcrystallization,
The amount of bound hydrogen in the film is greatly reduced, and usually becomes about 3 atom%. Also, for the film that has undergone microcrystallization,
Since the movement of hydrogen in the film is limited, structural changes due to exposure to hydrogen plasma cannot be expected.

Further, when the amount of hydrogen in the film exceeds 25 atomic%, the film is formed by a chemical vapor deposition method to form an amorphous semiconductor thin film at a low temperature close to room temperature, and ion implantation is performed. It is not preferable for a device or the like because it is necessary to forcibly implant hydrogen into the film. In addition,
It is possible to form a thin film in which the amount of hydrogen contained in the film exceeds 25 atom% under conditions close to room temperature, but in the film growth process there are sufficient film-forming radicals for forming the film. Can not migrate on the surface. In this case, since a large amount of hydrogen is already present in the film, it is no longer possible to expect an effect such as defect compensation by causing hydrogen to enter the film by exposure to hydrogen plasma. It ends up. Therefore,
In the method of forming a film by the chemical vapor deposition method using hydrogen or a metal hydride compound gas containing an inert gas, the amount of bonded hydrogen in the film formed is less than 25 atomic% and 5 atomic%
The above is preferable.

In the case of forming an amorphous silicon thin film, the suitable film forming temperature range is limited. In order for the amount of bonded hydrogen in the film of the amorphous semiconductor formed by the chemical vapor deposition method to be less than 25 atomic% and 5 atomic% or more, the film forming temperature range must be less than 385 ° C. and 100 ° C. or more. preferable.

Further, the thickness of the thin film formed in one film forming step by these chemical vapor deposition methods is 1 nm.
It is preferably 6 nm or less and more preferably 2 nm or more and 5 nm or less. When the film thickness formed by one film forming step is too thin and less than 1 nm, excess hydrogen is supplied into the film, and the desired high-quality amorphous semiconductor thin film cannot be formed. . Further, when the film thickness formed by one film forming process is much thicker than 6 nm, exposure to hydrogen plasma results in insufficient penetration of the supplied atomic hydrogen in the process. Will end up. In the present invention, the amount of atomic hydrogen generated during the discharge of hydrogen gas and supplied to the surface of the substrate is 1 × 10 ¹⁵ pieces / cm ² or more 5
It is preferably × 10 ¹⁵ cells / cm ² or less.

Now, FIG. 1 is an observation of the conductivity and photosensitivity of the film obtained according to the difference in the supply amount of atomic hydrogen. It can be seen that the photosensitivity is low when the supply amount of atomic hydrogen is less than 1 × 10 ¹⁵ cells / cm ² . On the other hand, when the supply amount of atomic hydrogen is more than 6 × 10 ¹⁵ cells / cm ² , a sharp increase in the conductivity of the amorphous thin film was confirmed, and it was judged that crystallization occurred. To be done. Thus, the important point of the method of the present invention is that the supply amount of atomic hydrogen itself is important. If the permeation of hydrogen by exposure to hydrogen plasma is carried out by the diffusion of atomic hydrogen, it should be greatly affected by the film formation temperature. Figure 2 shows W.Beyer J.Appl.Phys. 53, 8
735 (1982), M. Reinelt J. Non-Cryst. Solid59 & 60, 1
69 is a plot of the hydrogen diffusion coefficient, as measured by 69 (1983), as the reciprocal of absolute temperature.

Therefore, the most preferable thin film type according to the present method
The growth temperature range is 160 ° C to 200 ° C.
The diffusion constant of hydrogen in the range is 2 × 10^-20cm²/ s or more 2
× 10 ^-18cm²It is less than / s. For example, in the method of the present disclosure
Diffusion constant of hydrogen in a suitable temperature range of 2 × 10^-18c
m²In the case of / s, since this value is extremely small,
20 seconds from surface hydrogen at a position 4 nm deeper than the surface
After that, the hydrogen concentration is extremely different from the surface hydrogen concentration.
It is expected to be low. Therefore, hydrogen diffusion
It is clear that this is not the essential effect of the law. Therefore,
It is conceivable that at a depth of a few nm from the film surface
Has a sufficient network of constituent molecules that make up the membrane structure.
I think it's in a chaotic state, not solidified.
Is to say. In such a region,
The given atomic hydrogen easily penetrates and alters the membrane structure.
It is possible that he has made it happen. What
The supply energy density in the film formation process and film formation pressure
And the RF power density in the process of exposure to hydrogen plasma
It may be different from the film forming pressure condition.

That is, in the film forming step, the conditions for forming a normal amorphous semiconductor may be used. For example, in the case of a film forming method using RF plasma, a suitable supply energy density is preferably 0.01 W / cm ² or more and 1 W / cm ² or less, and the film forming pressure is 10 mTorr or more and 1 Torr or less. Is desirable. On the other hand, in the step of exposing to hydrogen plasma, the RF power density is 0.01
It is desirable W / cm ² or more and 1W / cm ² or less, the film deposition pressure is desirably 1Torr or less than 10 mTorr.

In the present invention, the amount of atomic hydrogen generated during discharge consisting of hydrogen gas and supplied to the expected surface is 1
It is desirable that it is not less than × 10 ¹⁵ pieces / cm ^{2 and not} more than 5 × 10 ¹⁵ pieces / cm ² . The amount of atomic hydrogen supplied to the surface of the substrate is measured as follows. That is, on the glass substrate,
A tungsten oxide thin film is formed using the electron beam evaporation method. When this tungsten oxide thin film is inserted into hydrogen plasma, the absorbance changes due to hydrogenation reaction due to atomic hydrogen. This change was evaluated by a spectrophotometer, and the absorbance and half-value width of the absorption spectrum were calculated using the following SMAKRA.
By substituting into the equation, Nf = 0.87 × 10 ¹⁷ n (n ² +2) ⁻² (kmaxL) W _1/2 , the amount of atomic hydrogen reaching the substrate surface can be estimated. Where N is the number of color centers (cm
^-2 ), n is the refractive index of tungsten oxide (= 2.5), kmaxL is the absorbance of the peak, W1 _{/ 2} is the peak half width, and f is 0.1.

FIG. 3 shows that the hydrogen flow rate is 10 sccm and the pressure is
Power 0.15 Torr, RF power density 0.64 W / cm ²Formed under the conditions
Do not expose the above tungsten oxide thin film to hydrogen plasma.
This is a plot of the time change due to and. Figure 3
Therefore, the hydrogen plasma exposure time is approximately linear for up to 10 minutes.
It can be seen that the amount of child hydrogen is increasing. Even longer
Upon exposure, the increase is saturated, but
As the hydrogenation reaction of tungsten saturates,
The amount of hydrogen is not saturated. Therefore, the inclination of the straight part
The amount of atomic hydrogen supplied in a unit time is calculated.
You can

The supply rate of atomic hydrogen obtained from the straight line portion of FIG. 3 is the RF power density of 0.64 W / cm ² which is the above condition.
Under the above conditions, it was 1 × 10 ¹⁴ cells / cm ² / sec. Furthermore, hydrogen flow rate 10 sccm, pressure 0.15 Torr, RF power density
When the atomic hydrogen supply rate was similarly obtained when exposed to hydrogen plasma formed under the condition of 0.13 W / cm ² ,
It was 4 × 10 ¹³ pieces / cm ² / sec. Therefore, FIG. 4 is a plot of the atomic hydrogen supply rate with the square root of the RF power density as the horizontal axis. The atomic hydrogen feed rates obtained at the two RF power densities can be approximated by a straight line passing through the origin. Thus, the supplied atomic hydrogen supply amount can be uniquely determined by the square root of the RF power density. From the results of FIGS. 3 and 4,
It has been revealed that the amount of atomic hydrogen supplied can be controlled by its RF power density and time.

Next, FIG. 5 shows a basic structure of a preferable apparatus for carrying out the present invention. That is, this apparatus has a two-layer structure of the film forming chamber 1 and the substrate preparation chamber 2. The film forming chamber 1 and the substrate preparation chamber 2 are connected by a gate valve 8. The substrate preparation chamber has a heater 5 for heating the substrate, a power source for supplying electric power to the heater,
And a turbo molecular pump 21 and a rotary pump 22 for evacuation. With this evacuation system, the substrate installed in the substrate preparation is heated by the heater and is evacuated to prepare for film formation.

An RF electrode 3 is provided in the film forming chamber 1 and an electric discharge is formed between the RF electrode 3 and the substrate heater 4. The RF electrode 3 is
Electric power is applied by the high frequency power supply 31. Electric power is applied to the heater 4 by the heater power supply 41. The substrate 9 is placed on the heater, and heated and heated by the heater. In addition, this film formation chamber 1 has a turbo molecular pump 11
And is evacuated by the rotary pump 12,
The pressure in the film forming chamber can be adjusted by the conductance valve 13. The gas for film formation is supplied and controlled by the mass flow controllers 71, 72 and 73, the gas of which the flow rate is controlled.

An important point of this apparatus is that it has an RF discharge electrode for forming hydrogen plasma, in addition to the film forming mechanism. In the case of the film forming apparatus in FIG. 3, since the film forming method using the RF discharge electrode is used also in film forming, the film forming step and the step of exposing to hydrogen plasma can be performed by the same system. By performing this method, the amount of bonded hydrogen existing in the film tends to increase. Along with this, for example, in the case of a hydrogenated amorphous silicon thin film, the amount of bound hydrogen in the film increases and the optical band gap thereof tends to widen. This is because active atomic hydrogen is effectively supplied into the film,
By this method, hydrogen can be effectively supplied to dangling bonds in the film, which is not controlled by the ordinary film forming method, and as a result, the defect density can be greatly reduced. FIG. 6 compares the change value of the amount of bonded hydrogen in the film, which is increased by the exposure to the hydrogen plasma, with the degree of reduction of the defect density. As a result, it is recognized that the greater the increase in the amount of bonded hydrogen in the film, the more effective the reduction in defect density.

As described above, by directly controlling the hydrogen content and the hydrogen bond morphology in the hydrogen film, it becomes possible to freely design the optical band gap of the amorphous thin film, and at the same time, the thin film can be formed by reducing defects. It will be possible to achieve higher quality. As a result, the conversion efficiency of the thin-film solar cell, especially the open-ended voltage and the fill factor are improved. Hereinafter, an example of an embodiment of the present invention will be described with reference to examples.

[0029]

【Example】

(Example 1) The apparatus used for forming the thin film is the same as the apparatus shown in FIG. In Example 1, monosilane gas was used as a raw material gas for film formation. The flow rate of the monosilane gas is 10 sccm, and is flown through the mass flow controller 71 in FIG. The film forming temperature in this system is 175 ° C. Then, the film is formed so as to have a predetermined film thickness, but in the present embodiment, the film thickness per one time was 4 nm. When the RF discharge ends, the film formation is stopped and the gas supplied to the chamber is stopped. Then, the evacuation is started with the main valve opened to 10 ^-6 Torr or less.

Next, the step of exposing to hydrogen plasma is started. First, while supplying hydrogen, pressure control is performed to adjust to 150 mTorr as in film formation. Then, RF discharge is performed. The RF power density at this time is 0.64 W / cm ² . The operation of exposing to hydrogen plasma for a predetermined time was performed, the discharge was stopped again, the flow rate of hydrogen gas was stopped, and vacuuming was performed until the pressure became 10 ⁻⁶ Torr or less as in the case of the end of the film forming process. By repeating these series of steps,
This operation was repeated until a predetermined film thickness (300 nm or more) was obtained.

FIG. 7 shows a state in which the defect density is decreased with the supply amount of atomic hydrogen as the horizontal axis. From this result, it is recognized that the film characteristics of the film are largely changed depending on the supply amount of atomic hydrogen. The discharge power density of RF is 0.64 W / cm ² , and the supply rate of atomic field hydrogen at this time is 1 × 10 ¹⁴ / cm ² / s. As a result of this examination,
It can be seen that the film characteristics change significantly depending on the increase in the time of exposure to hydrogen plasma. The defect density in the film decreases as the exposure time to hydrogen plasma increases. Furthermore, it was confirmed that when the time of exposure to this hydrogen plasma exceeded 60 seconds, crystallization occurred and a marked increase in dark conductivity began. At this time, the supply amount of atomic hydrogen reached 6 × 10 ¹⁵ pieces / cm ² .
It can be seen from FIG. 7 that the supply amount of atomic hydrogen, which is effective in reducing the defect density, is 2 × 10 ¹⁵ cells / cm ² or more and 4 × 10 ¹⁵ cells / cm ² or less. As described above, it was confirmed that the quality of the amorphous silicon thin film was improved by the method of the present disclosure.

(Example 2) An apparatus used for forming a thin film is
It is the same as the device shown in FIG. In Example 2, as in Example 1, monosilane gas was used as the raw material gas for film formation. The flow rate of monosilane gas was 10 sccm, and the procedure for forming the film was the same as in the case of Example 1. However, in the second embodiment, the change in the film characteristics when the film formation temperature is changed is shown.

FIGS. 8 and 9 show the difference in film forming temperature.
This is a comparison of the differences in film characteristics. For comparison, the characteristics of the film formed by the ordinary film forming method at each temperature are shown for comparison. As a result, it can be seen that the characteristic changes greatly differ depending on the film forming temperature. As the temperature increases, the amount of increase in the amount of bound hydrogen in the film decreases. Desorption of hydrogen from the film-forming surface is a function of temperature, and the higher the temperature, the higher the hydrogen desorption rate. As a result, the desorption rate of hydrogen from the film-forming surface at 385 ° C. is expected to be much higher than that at 175 ° C. Therefore, the supply of atomic hydrogen generated by hydrogen plasma is It is thought that this is the result of being unable to catch up with the departure.

On the contrary, when the temperature is low, a large amount of bound hydrogen is already present in the film, and the increase of bound hydrogen due to hydrogen plasma becomes small. As a result, the decrease in defect density is small, and it is recognized that there is a substantially proportional relationship between the increase in the amount of bound hydrogen atoms and the degree of decrease in defect density.

(Embodiment 3) The apparatus used for forming the thin film is
It is the same as the device shown in FIG. In Example 1,
Monosilane gas and monogermane gas were used as raw material gases for film formation. The flow rate of monosilane gas was 5 sccm, and the flow rate of monogermane gas was changed for the purpose of forming different optical band gaps. 20 sccm of hydrogen was used as a diluting gas. In this embodiment, monogermane gas is caused to flow at a flow rate of 1 sccm through the mass flow controller 71 in FIG.
The monosilane gas was caused to flow at 5 sccm through the mass flow controller 72. The film forming conditions used were a substrate temperature of 17
The temperature was 5 ° C., and the film forming pressure was 150 mTorr. R
The F power density is 0.04 W / cm ² .

Next, in the step of exposing to hydrogen plasma, R
The F output density was 0.16 W / cm ² , and the same operation was performed at 150 mTorr. At this time, the supply rate of atomic hydrogen determined from FIG. 4 was 5 × 10 ¹³ pieces / cm ² / sec. Then, the time of exposure to hydrogen plasma was examined from 0 seconds to 120 seconds. FIG. 10 shows a state in which the electric conductivity and the photosensitivity are lowered with the supply amount of atomic hydrogen as the horizontal axis. From this result, it is recognized that the film characteristics of the film are largely changed depending on the supply amount of atomic hydrogen. FIG.
It can be seen that the supply amount of atomic hydrogen, which is more effective in reducing the defect density, is 2 × 10 ¹⁵ pieces / cm ² or more and 4 × 10 ¹⁵ pieces / cm ² or less. As described above, it was confirmed that the quality of the amorphous silicon thin film was improved by the method proposed by the present invention.

[0037]

By repeating the film forming step and the step of exposing to hydrogen plasma, the optical band gap of the amorphous thin film can be freely controlled by directly controlling the hydrogen content and the hydrogen bonding morphology of the amorphous semiconductor thin film. In addition to being able to be designed, it is possible to achieve high quality thin films by reducing defects. As a result, it is possible to improve the conversion efficiency of the thin-film solar cell, especially the open-circuit voltage and fill factor.

[Brief description of drawings]

FIG. 1 is a graph showing changes in the supply amount of atomic hydrogen, conductivity, and photosensitivity.

FIG. 2 is a graph showing the diffusion coefficient of hydrogen atoms in an amorphous silicon thin film.

FIG. 3 is a graph showing changes in atomic hydrogen amount with time of hydrogen plasma.

FIG. 4 is a graph showing the relationship between RF power density and atomic hydrogen supply amount.

FIG. 5 is an illustration of an apparatus for carrying out the present invention.

FIG. 6 is a graph showing the relationship between the amount of change in bound hydrogen and the defect density.

FIG. 7 is a graph showing the relationship between the supply amount of atomic hydrogen and the defect density in Example 1.

FIG. 8 is a graph showing the relationship between the film forming temperature and the amount of bound hydrogen in Example 2.

FIG. 9 is a graph showing the relationship between film forming temperature and defect density in Example 2.

FIG. 10 is a graph showing the relationship between the supply amount of atomic hydrogen and the electrical conductivity and photosensitivity in Example 3.

[Explanation of symbols]

 1 deposition chamber 2 substrate preparation chamber 3 cathode electrode 4 substrate heating heater (for deposition chamber) 5 substrate heating heater (for substrate preparation chamber) 6 viewing window 8 gate valve 9 substrate 11 turbo molecular pump 12 rotary pump 13 conductance valve 21 Turbo molecular pump 22 Rotary pump 31 RF power supply 41 Heater power supply 51 Heater power supply 61 Focusing device (emission analysis device) 62 Optical fiber (emission analysis device) 63 Analysis device (emission analysis device) 71 Mass flow controller 72 Mass flow controller 73 Mass flow controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shin Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (8)

[Claims] 1. A method for producing an amorphous semiconductor thin film, which comprises repeating a step of forming a semiconductor thin film by a chemical vapor deposition method using a thin film raw material gas and a step of exposing the thin film with a plasma of hydrogen gas. And the amount of atomic hydrogen supplied to the surface of the semiconductor thin film is 1 × by the step of exposing the thin film with plasma composed of the hydrogen gas.
A method for producing an amorphous semiconductor thin film, characterized in that it is not less than 10 ¹⁵ pieces / cm ^{2 and not} more than 5 × 10 ¹⁵ pieces / cm ² . 2. The amorphous semiconductor thin film according to claim 1, wherein the bound hydrogen content of the semiconductor thin film formed by the chemical vapor deposition method using a thin film raw material gas is 25 atomic% or less and 5 atomic% or more. Production method. 3. The method for producing an amorphous semiconductor thin film according to claim 1, wherein the thickness of the semiconductor thin film formed by a chemical vapor deposition method using a thin film raw material gas is 1 nm or more and 6 nm or less. . 4. The amorphous semiconductor thin film is a silicon hydride amorphous thin film, a hydrogenated germanium amorphous thin film, a hydrogenated carbon amorphous thin film, a silicon hydride germanium amorphous thin film or a non-hydrogenated silicon carbide non-crystalline thin film. It is a crystalline thin film, The manufacturing method of the amorphous semiconductor thin film in any one of Claim 1 thru | or 3 characterized by the above-mentioned. 5. The chemical vapor deposition method is a photo CVD method or a thermal C method.
The method for producing an amorphous semiconductor thin film according to any one of claims 1 to 4, which is a VD method, a plasma enhanced CVD method, a laser enhanced CVD method, or a reactive sputtering method. 6. The raw material thin film gas is a silicon hydride compound Si _n H _{2m + 2} , a hydrogenated germane compound Ge _n H _{2m + 2} , a hydrocarbon C _n H _{2m + 2} , or hydrogen of these compounds is chlorine. The method for producing an amorphous semiconductor thin film according to any one of claims 1 to 5, which is a compound or derivative substituted with an atom or a fluorine atom. 7. The method for producing an amorphous semiconductor thin film according to claim 2, wherein the source gas contains hydrogen or an inert gas. 8. The inert gas is He, Ne, Ar, Kr.
8. The method for producing an amorphous semiconductor thin film according to claim 7, wherein the rare gas is selected from Xe.